Aluminum nitride (AlN) ceramics are important heat-dissipation materials for high-power electronic devices. However, the high sintering temperature required by conventional processing routes limits practical application of AlN ceramics and increases fabrication costs. Therefore, it is necessary to develop preparation method that is capable of achieving densification at relatively low temperature. To address the difficulty of simultaneously obtaining high densification and high thermal conductivity in polycrystalline AlN ceramics under reduced-temperature sintering conditions, this work adopts a stepwise research strategy. First, the densification behavior and thermal conductivity of pure AlN under high-pressure assistance were investigated to identify the optimal sintering conditions. Under additive-free conditions, pure-phase AlN ceramics with clean grain boundaries and high densification were prepared at 5.0 GPa and 1400 ℃, achieving a thermal conductivity of 101.6 W/(m·K). Based on these optimized conditions, the AlN/diamond composite system was further studied, and the effects of diamond volume fraction on the structure and properties of the composites were systematically examined. The results show that the thermal conductivity of the composites first decreases and then increases with increasing diamond volume fraction, reaching 112.4 W/(m·K) at 33.3%. Mechanistic analysis indicates that interfacial thermal resistance dominates at low diamond contents, whereas at high diamond contents the enhancement of heat transport by thermally conductive diamond pathways becomes more significant. By taking full advantage of the processing benefits of high-temperature and high-pressure technology, this work achieves substantial improvement of AlN-based materials at temperatures lower than those required in conventional sintering, thereby providing a new route for the low-temperature fabrication of high-performance thermally conductive ceramics.

Diamond has emerged as a quintessential representative of next-generation semiconductor materials, owing to its ultra-wide bandgap, exceptional thermal conductivity, high breakdown field strength, and outstanding carrier mobility. It has thus attracted extensive attention from fields such as power electronics, radio-frequency communications, and quantum information technologies. Intrinsic single-crystal diamond serves as the foundational substrate for diamond semiconductor development, requiring impurity concentrations at the parts per billion (ppb) level and extremely low dislocation densities. While the high-pressure high-temperature (HPHT) method yields material of higher purity and superior crystal quality, its utility is limited by small crystal dimensions. Consequently, HPHT-grown diamond is frequently employed as a substrate for chemical vapour deposition (CVD) homoepitaxy, enabling the preparation of large-area, high-quality single crystals. Regarding doping, the boron (B) atom, with a size difference of merely 6.5% compared to carbon (C), readily incorporates into the diamond lattice, facilitating the production of high-performance p-type diamond. Related devices, such as Schottky barrier diodes, have been successfully demonstrated. In contrast, n-type doping presents a fundamental challenge: potential dopants like phosphorus (P) and sulphur (S) possess atomic radii 35%–57% larger than carbon, making their incorporation and activation within the lattice exceedingly difficult. The ultra-high pressure and high-temperature diffusion method, which modulates this atomic size disparity under extreme pressures (e.g., about 15 GPa), emerges as a promising new pathway towards achieving shallow-level n-type doping. Concerning surface terminations, hydrogen termination induces a high-mobility two-dimensional hole gas (2DHG), whilst oxygen termination enhances interface stability and provides chemical passivation. However, their thermal stability windows (approximately 400 and 600 ℃, respectively) remain inferior to those of substitutionally doped diamond, limiting their application in high-temperature and high-frequency devices. Therefore, breakthroughs in n-type doping, enhanced thermal stability of surface terminations, and the development of large-area, cost-effective fabrication processes are critical to advancing diamond semiconductor technology towards commercialisation in power electronics, quantum technologies, and high-performance sensing. This review aims to analyse and discuss these pivotal issues, exploring both the prospects and the persistent challenges facing diamond semiconductor development.

As an important type of powder metallurgy products, tungsten carbide-cobalt (WC-Co) cemented carbides are widely applied in numerous industrial fields. Traditional sintering methods suffer from high sintering temperatures, long sintering times, and grain coarsening, which make it difficult to meet the requirements for the preparation of high-strength fine-grained cemented carbides. In this study, the sintering behavior of the sub-micron WC-5Co (with a mass fraction of cobalt of 5%) cemented carbides was investigated using the high-temperature and high-pressure (HTHP) method. The experimental results show that the sintered body can achieve a relative density of 99.4% and a Vickers hardness value of (24.0±0.3) GPa under the treatment conditions of 5.0 GPa and 1 250 ℃, which is significantly better than that of the same composition of cemented carbides prepared by spark plasma sintering (SPS) and vacuum sintering methods. In comparison with the commercial cemented carbides with the same initial powder, the average grain size of WC in the sintered samples under high-temperature and high-pressure conditions is reduced by about 36%, and the Vickers hardness is increased by about 10%. In comparison with traditional sintering methods, the HTHP sintering method effectively reduces the sintering temperature, shortens the sintering time, and enhances sintering efficiency. Moreover, high pressure can effectively inhibit the abnormal growth of the WC grains during solid-state sintering. During liquid-phase sintering (at 1 450 ℃), an increase in sintering pressure results in significant refinement of the WC grains. When the sintering pressure is increased from 3.0 GPa to 5.0 GPa, the Vickers hardness of the samples is increased by about 7%.